23 research outputs found

    Raptor and wading bird migration in Veracruz, Mexico : spatial and temporal dynamics, flight performance, and monitoring applications

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    The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on October 9, 2007)Vita.Thesis (Ph. D.) University of Missouri-Columbia 2007.This dissertation is organized in four chapters that deal with different aspects of my long-term studies of migratory raptors, vultures, and wading birds, in central Veracruz, Mexico, during the course of three spring and ten fall seasons (1991-2004). The first chapter is a descriptive piece with a discussion of the role of regional topography and altitudinal distribution of thermal convection in the formation of a geographic bottleneck for soaring migrants. I examine several characteristics (such as flocking behavior and flight mode) of an assemblage of migratory birds composed of 33 species of nine families in order to understand why these birds are funneled through this area. I also describe the magnitude of these migrations, their inter-annual variation, flocking behavior, and flight mode, and briefly discuss issues related to their stopover ecology and conservation. One of the outstanding findings of this project is documenting the migration of over 0.8 million birds in spring and over 5.1 million in fall, the most important migratory flyway for raptors in the World. These migrations are dominated by seven species: American White Pelican (Pelecanus erythrorhynchos), Anhinga (Anhinga anhinga), Wood Stork (Mycteria americana), Turkey Vulture (Cathartes aura), Mississippi Kite (Ictinia mississippiensis), Broad-winged Hawk (Buteo platypterus), and Swainson's Hawk (B. swainsoni). The migration bottleneck is a result of two features of the regional landscape. Flights are limited to the east by the Gulf of Mexico, and to the west by the availability of thermal convection. Thermal convection decreases as elevation increases, and is higher in spring than in fall. Stronger thermal convection limits our ability to record migration: it contributes to variation in geographic distribution patterns, altitude of flight, and overall conditions for migration recording. The second chapter presents a quantitive description of the temporal dynamics of an assemblage of one species of vulture and 11 species of diurnal raptors and uses these measures of intra- and inter-annual variation to make some inferences about the effects of variables at multiple scales in species' migration patterns. I also use this information to evaluate the implications of these temporal variations on long-term monitoring schemes. The patterns I present are a species-by-species description of spring and fall migration, and a characterization and quantification of the structural patterns of the complete assemblage. During spring, migration is unimodal in seven species and has a bimodal/unclear distribution pattern for five species. Species' migration through the region lasted between 43 and 70 days (mean=53 days). The migration season of four species is significantly shorter in spring than in the fall. I found significant differences in timing of migration across years for all species, with peak dates differing between 3-11 days. In fall, migration is unimodal for ten species. Mean duration of fall migration recorded ranges between 20-74 days (mean=52 days). The duration of fall migration was significantly shorter than spring for five species. With no exceptions, all species had significant differences in timing of migration across years, with peaks differing between 4-9 days. The third chapter examines the differential flight performance among species and migration seasons. I studied the behavior of nine species of large soaring birds and quantified their wing beat frequency, a commonly used measure of flight performance. There are significant differences among species' wing beat frequency, and larger birds tend to require less energetic expenditure in their flights. I also found seasonal differences in wing beat frequency in seven species, and, contrary to my predictions, spring is a season that demands higher energetic expenditure (higher wing beat frequency) for more species than fall. My last chapter covers the topic of using of migration count data from Veracruz to assess population trends of New World vultures and diurnal raptors. I evaluated the use of migration counts to monitor populations and obtained annual estimates of population change for five species over a 10-year period. In those five species, who meet both an a priori accuracy target goal and the assumptions of a recently developed regression method, I found significant population increases. The populations of Turkey Vulture (Cathartes aura), Osprey (Pandion haliaetus), Cooper's Hawk (Accipiter cooperii), Broad-winged Hawk (Buteo platypterus), and Swainson's Hawk (Buteo swainsoni) have been increasing at a rate between +1.6 and +11.1% year-1 and a mean cumulative increase of 26% between 1993-2004. I was unable to assess population trends in 28 species that had very high coefficient of variation In annual counts, less than 100 individuals recorded per field season, and/or shorter field coverage of their migration period. What is significant in my research is the generation of baseline information on raptor, vulture, and wading bird migration ecology from one of the very few sites in the Neotropics where a long-term research and monitoring program has been sustained. This research has some immediate conservation applications, particularly the use of systematic migration counts to monitor the populations of many species.Includes bibliographical reference

    Feeding rates of raptors during autumn migration in the Central Appalachians 1987–2022

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    Migratory raptors can fuel their journeys by feeding along the way. To maximize migration success, raptors are suspected to time their movements with the availability of their prey. Feeding rates can vary among species depending on migration distance (long vs. short distance), flight strategies (flapping vs. soaring), and within species according to individual timing (early vs. late migrants). We assessed the feeding rate of four eastern North American migratory raptors over a period of 35 years. Using visual observations collected during autumn migration in the Central Appalachians, we assessed the presence/absence of distended crops of migrants. We quantified the feeding rates of species with different migration ecologies (migration distance, flight strategies), compared within-season (timing) species, and assessed if feeding rates varied over the last 35 years. We found a higher feeding rate in short-distance than in long-distance migrants and in power-flapping vs soaring migrants. We detected a long-term significant increase in feeding rate for most species, more evident in early migratory individuals coupled with a decrease in the feeding rate of late migrants. Understanding how feeding rates vary according to migratory behavior and how the migration ecology of raptors is changing under a scenario of global environmental change is important for their conservation

    Dinámica de uso y cobertura del suelo en un parque nacional mexicano

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    To understand the dynamics of land cover at the Parque Nacional Cofre de Perote, the rates of change in land use were compared at two different scales during the period 1995-2004. At the meso scale, these patterns were studied throughout the entire Parque Nacional Cofre de Perote, which is one of the 60 priority mountains of Mexico, and an important natural protected area of the country located in the state of Veracruz. At a micro scale, the work was focused in ejido El Conejo, located within the boundaries of this national park. Federal government digital orthophotos were used to determine changes in nine categories of land use. In both, the meso- and micro-scale, it was found that the predominant land cover categories are agriculture and forest. The probabilities of land cover change at both scales are low and essentially the same for most land use categories, reflecting both small gains in forest cover park-wide as well as the effectiveness of the ejido in managing natural resources within the park. The authors consider that the findings of the study may be applicable to the broader situation of national parks in Mexico and, finally, the importance of integrating local stakeholders in the management of natural protected areas is discussedPara entender la dinámica de la cobertura del suelo en el Parque Nacional Cofre de Perote, se hizo una comparación de las tasas de cambio de uso a dos escalas durante el periodo 1995-2004. A escala meso, se estudiaron estos patrones en toda la superficie del Parque Nacional Cofre de Perote, que es una de las 60 montañas prioritarias de México y también una importante área natural protegida del país ubicada en el estado de Veracruz. A escala micro el estudio se enfocó en el ejido El Conejo que se encuentra dentro de los límites de este parque nacional. Se utilizaron ortofotos digitales del gobierno federal para determinar el cambio en nueve categorías de uso del suelo. En ambas, meso y microescalas, se encontró que las categorías predominantes de cobertura son la agricultura y el bosque. Las probabilidades de cambio de cobertura del suelo en ambas escalas son bajas y tienen valores esencialmente iguales para la mayoría de las categorías de uso, reflejando tanto pequeñas ganancias en cobertura forestal en todo el parque como la efectividad del ejido en el manejo de recursos naturales dentro del parque. Se considera que los hallazgos de este estudio pueden ser aplicables a la situación prevaleciente en los restantes parques nacionales de México; al final se discute la importancia de integrar a los actores locales en el manejo de áreas naturales protegidasS

    Cambios en las poblaciones de aves rapaces migratorias en Veracruz, México, 1995-2005.

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    Migration counts of raptors have been used as a valid technique to assess population levels. Counts from Veracruz, Mexico, have the potential of generating valuable information for regional- to continental-scale populations of some species and to provide coverage for others that are not monitored elsewhere. This paper evaluates the use of Veracruz migration counts to monitor populations, documents the adjustments made to a currently existing method to analyze migration count data and fit it to the specific properties of our dataset, and presents estimates of population change over a decade. We used long-term, effort-adjusted migration count data to generate annual indexes of abundance. The series of annual indexes is fitted to a polynomial regression to produce an estimate of the annual rate of change. The use of this methodology with Veracruz data shows its usefulness to datasets of many species, as well as limitations to datasets from species with high interannual variation in migration counts, and those recorded rarely. In seven species, the authors found significant population change. Six of them, Swallow-tailed Kite, Mississippi Kite, Cooper’s Hawk, Swainson’s Hawk, Zonetailed Hawk, and Peregrine Falcon show increases at an annual rate between 1.9-15.7% per year-1 in the period 1995-2005. One species, the Northern Harrier, is decreasing at a rate of -8.4% year-1 during the same period. Trends reported here reveal population increases in most cases, and concur with the pattern found in migration counts from surveys such as the Breeding Bird Survey and the Christmas Bird Count.Los censos durante la migración han sido utilizados como una herramienta válida para determinar estatus poblacionales de aves rapaces. En Veracruz, México, éstos tienen la posibilidad de generar valiosa información sobre poblaciones a escala regional y continental, y de proveer cobertura para aquellas que no son estudiadas en otros sitios. Los objetivos de este trabajo son evaluar el uso de los censos durante la migración en Veracruz para seguimiento de poblaciones, documentar los ajustes hechos a un método de análisis existente para hacerlo apropiado a las propiedades específicas de nuestros datos y presentar estimaciones de cambio poblacional de las especies a lo largo de una década. Esta metodología utiliza censos de la migración de rapaces a largo plazo ajustados a esfuerzo de muestreo para generar índices anuales de abundancia. La serie de índices anuales es ajustada a una regresión polinomial para producir una estimación de la tasa de cambio anual. El uso de esta metodología de análisis para los censos en Veracruz demostró su utilidad para determinar tendencias poblacionales en muchas especies, así como limitaciones en aquellas con gran variación interanual en los censos y en especies registradas raramente. Se encontraron cambios poblacionales significativos en siete especies. Seis especies, Elanoides forficatus, Ictinia mississippiensis, Accipiter cooperii, Buteo swainsoni, B. albonotatus y Falco peregrinus muestran incrementos a una tasa anual entre 1.9-15.7% por año-1 en el periodo 1995-2005. Una especie más, Circus cyaneus, registró descensos a una tasa de -8.4% por año-1 en el mismo periodo. Las tendencias poblacionales que se reportan aquí confirman en su mayoría incrementos poblacionales y coinciden con los datos de fuentes como los Censos de Aves Reproductoras o los Censos Navideños de Aves

    DATA_pilosocereus_leucocephalus_frugivory_records

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    Records of frugivory of Pilosocereus leucocephalus by birds and bat

    Data from: Patterns of frugivory in the columnar cactus Pilosocereus leucocephalus

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    In the frugivory networks of many arid and semi-arid Mesoamerican ecosystems, columnar cacti act as keystone species that produce fruits with a high content of water and nutrients attractive to numerous vertebrates. The aim of this investigation was to assess the fruit removal patterns of two guilds of frugivores on the fruits of the woolly torch Pilosocereus leucocephalus. We assessed fruit pulp removal in two ways: by estimating the consumption of seeds given the amount of pulp removed per visit and by estimating the percentage of pulp removal over time. We put exclosures on unripe, intact fruits to keep frugivores from removing material. Once ripe, we removed the exclosures and tracked animal visitation of 69 fruits using camera traps. We obtained a total of 2162 h of footage (14:47 h of them with effective pulp removal). The highest number of visitors is that of diurnal species (n=12, all birds) vs. only four nocturnal (three bats, one rodent). The most effective species in pulp removal are birds. Bats play a modest role in frugivory of this cactus. The significance of this work is two-fold: (1) birds and bats consume the fruit pulp of this cactus and likely disperse its seeds, and (2) although bats rank high in pulp removal effectiveness, birds as a guild far outweigh their importance in this system, as they are not only more frequent but also remove more pulp and seeds. Both groups are known to be important in cacti seed dispersal, and our findings are essential in understanding the population dynamics of the woolly torch and in elucidating its seed dispersal ecology
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